In the irradiation of large-surface targets, it is known to provide an ion source, from which ions are extracted by means of an extrusion system involving acceleration of the ions. The ions can then be separated by mass in a magnetic dipole and the resulting substantial monoenergetic ions from the monochromatry formed by the magnetic dipole are accelerated to form a monoenergetic beam of ions.
The monoenergetic beam of ions is generally focussed and trained upon a surface to be irradiated which is located in the ion-beam path and is rotatable about the axis of the accelerating and focussing devices.
In the past, when the focussed beam was trained upon the surface to be irradiated, it was necessary to provide a lateral movement of the rotating surface so that the focal point on the surface against which the ions were directed could be scanned or swept across the surface to provide as uniform as possible an irradiation of the surface. Current density of the beam was thereby held constant.
A disadvantage of this system is that with a constant ion irradiation dose delivered by the beam, temperature peaks can develop on the irradiated surface which can lead to undersirable diffusion and internal stress phenomena. This can only be limited in the prior art approach by a relatively low mean working temperature, i.e. limiting the current density.